*Update* Coast Guard investigating a sheen off the coast of Grand Isle, Louisiana

Sunday evening the U.S. Coast Guard reported samples taken from the sheen and analyzed by labs appeared to have “only trace amounts of petroleum hydrocarbons, oil and grease. …. At this point, the dark substance is believed to be caused by a tremendous amount of sediment being carried down the Mississippi River due to high water, possibly further agitated by dredging operations.”

Some of the substance has started to come ashore at Elmer Isle, Fourchon Beach and Grand Isle. The Coast Guard has hired ES&H to begin cleaning up the impacted shorelines and has boom standing by to deploy if needed.

As of Sunday night the Coast Guard said it did not believe the substance was related to last summer’s Deepwater Horizon spill.

A spokeswoman for W&T said Monday morning the company’s Matterhorn facility was not leaking and had no role in the incident.

+++++

The U.S. Coast Guard is investigating a 5-mile-wide sheen spotted on the surface of the Gulf of Mexico off the coast of Grand Isle, La.

A rainbow sheen was first reported at about 9:34 a.m. Saturday, with two more reports following, including one that said the sheen extended from six miles off the coast of Grand Isle to 100 miles out into the Gulf.

A Coast Guard helicopter was able to confirm there was a substance on the surface but was diverted for a search and rescue case and unable to investigate further, according to a statement from the Coast Guard.

The Coast Guard Cutter Pompano has been sent to the scene to gather a sample, but Petty Officer Casey Ranel said late Saturday it wasn’t clear if the ship would be able to complete its work in the dark.

Eileen Angelico, a spokeswoman for the Bureau of Ocean Energy Management, Regulation and Enforcement, said in an e-mail Saturday her agency is awaiting notification from either the Coast Guard or an operator before deciding whether it will send its own inspectors offshore to investigate. Such a decision will most likely be made Sunday morning, she said.

A number of other online items on Saturday seem to indicate the spill is beginning in a different area, however, the block known as Mississippi Canyon 243. That’s the location of the Matternhorn platform, which serves a tie-in for a number of different fields in the ara.

Calls to Matterhorn’s operator, W&T Offshore, were not returned as of Saturday night.